Strip tensioning apparatus



INVENTORS Sept. 25, 1951 M. D. STONE ET AL STRIP TENSIONING APPARATUSFiled June 8, 1948 patented Sept. 25, 1951 STRIP TENSIONIN G APPARATUSMorris D. Stone and Joseph I. Greenberger, Pittsburgh, Pa., assignors toUnited Engineering & Foundry Company, Pittsburgh, Pa., a corporation ofPennsylvania Application June 8, 1948, Serial No. 31,818

. 3 Claims.

The invention relates to apparatus for tensioning strip metal bydeflecting it upwardly into a loop as it passes between the rolls ofadjacent stands of a tandem or a continuous strip-rolling mill.

It is known that in the continuous rolling of strip metal the length ofthe strip between the bites of adjacent pairs of rolls may vary, due,among other things, to the relative peripheral speeds of the rolls, andto variations in the thickness, heat and other factors and properties ofthe strip from its leading to its trailing end. Because of this, it isdesirable to maintain the strip under tension between the bites ofadjacent pairs of rolls, which has beendone by various forms ofapparatus, known as tensiometers, that exert controlled upward pressureon strip metal to deflect it upwardly.

The object of the invention is to provide an improved tensiometer thatis simple in construction, and in the operation of which it effectivelymaintains a substantially constant tension on the strip when deflectedupwardly in a loop that varies materially in height.

The apparatus provided according to this invention comprises a pair ofstruts that may be either single members or frame-like structures, theadjacent ends of which are pivotally connected to an idle roller thatlies below strip metal as it passes from one to another of adjacentpairs of rolls, and that extends transversely of the strip. The rolleris preferably positioned substantially midway between the adjacent pairsof rolls, and the struts extend laterally and downwardly from it, 'onetowards one pair of rolls and the other towards the other. The lowerends of the struts are pivotally supported in fixed positionsproximateto the points of upward deflection of the strip, thearrangement being such that each strut lies substantially parallel tothe strip when it is variably deflected upwardly by the roller.

Preferably only one of the two roller-supporting struts is extensible,but both may be. The extensible strut, or each of the two if both areextensible, includes means for applying a constant force to itsextensible parts acting in a line passing through the pivoted ends ofthe strut.

The invention is diagrammatically illustrated in the accompanyingdrawings of which Fig. 1 is an elevation of the apparatus showing stripmetal being deflected or looped upwardly as it passes from one toanother roll, in which the fixed pivot axis of the outer endof eachstrut is below the point of upward deflection of the strip and insubstantially vertical alignment with it, and in only one strut isextensible; Fig. 2 a force diagram of the apparatus shown in Fig. l; andFig. 3 a force diagram of apparatus similar to that shown in Fig. 1, butin which the fixed pivot axis of the outer end of each strut is at oneside of the point of upward deflection of the strip.

Having reference first to Fig. 1, strip metal I is shown as being loopedor deflected upwardly by an idle roller 2 that is positionedsubstantially midway between two rolls 3 and 4, which may be the upperworking rolls of two stands of striprolling mills, or may be idle rollspositioned between two such mills. Roller 2 is supported by two struts 5and 6 whose adjacent ends are pivotally connected to the roller or to aframe that supports it. Strut 5 preferably comprises a pressure cylinder1 and a pistonrod 8 provided with a piston 9 within the cylinder,pressure fluid being applied to the rear of the piston through a pipe I4that is provided with a control valve l0 and a pressure indicator H. Thelower end of strut 5 is pivotally supported by a horizontal trunnion [2attached to cylinder 1, the axis of the trunnion being vertically belowthe axis of roll 3 and substantially vertically below the point ofupward deflection of strip l as it passes below roll 3. The lower outerend of rigid strut 6 is similarly pivotally supported at 13 in a fixedposition below roll 4, and the vertical distance between points ofupward deflection of strip I and the pivot points [2 and I3 of struts 5and 6 is equal to the radius'of idle roller 2.

For balancing the weight of the roller and strut apparatus and also, ifdesired, the weight of the strip passing over roller 2, such roller ispivotally connected to the upper end of a vertically disposed piston rodl5 whose lower end is connected to a piston l6 in a vertically disposedpressure cylinder I! which is pivotally supported in a fixed position bya horizontal trunnion l8. Pressure is supplied to the lower end ofpiston [6 through a pipe 19 that is provided with a control valve 20 anda pressure indicator 2|. By applying a predetermined constant pressureto the rear of the piston IS in cylinder ll, the dead weight of thestrut and roller apparatus and of the strip passing over the roller maybe balanced.

-As has been stated, by applying a constant uniform pressure to the backof piston 9 in extensible strut 5, a substantially constant tension ismaintained in strip I throughout a wide range of upward looping ordeflection of the strip. This appears from a consideration of the forcediagram of the Fig. 1 apparatus shown in Fig. 2, in which strip I has atension T effected by a pressure P applied to roller 2 by the extensiblestrut 5, resulting in a vertical upward pressure R on roller 2. Withnegligible variations within the practical range of vertical movement ofroller 2, the vertical distance it between the axis of roller '2 and ahorizontal line 25 passing through the lower pivots I2 and I3 of strutsand 6 is the same as the vertical distance h between the line oftangency of the strip with roller 2 and a horizontal line 26 passingthrough the lines of tangency of the strip with rollers 3 and 4.Similarly, angle a. between line 25 and the longitudinal axial line ofstrut 5 is the same asangle a between line 2'6 and the plane of theinclined portion of strip I.

Under these conditions, and taking into consideration the fact that-thetension in the strip pulls Vertically downward and the struts pushvertically upward on both sides of roller 2, the vertical pressure R.exerted on roller 2 by the struts, and by roller 2 to the strip, isequal to 2P sin .a, and the like pressure R exerted by the strip is 2Tsin a. Since the angles a and a are the same for all practical positionsof roller 2, it follows that T equals P. Hence, the amount of constantpressure P that is required may be determined by. multiplying thecross-sectional area of a given strip by the pounds per square inch oftension desired to be maintained in the strip as it passes betweenadjacent roll stands.

If in the tensioning apparatus shown in Fig. 1 the rolls 3 and 4 are theupper working rolls of two adjacent roll stands, instead of being idlerolls positioned between the working rolls in the line of pass betweenthem, it is necessary to pivotally support the lower ends of struts 5and 6 at the outsides of the roll stands to avoid interference with thelower rolls of the mill. Because in such an arrangement the tensioningapparatus interferes with free access to the mills, in most cases it isundesirable thus to support the struts.

In the force diagram shown in Fig. 3, the fixed pivot point of the lowerend of each of the struts 5' and 6 is positioned proximate to the upperworking roll at a side of it, and when so positioned it can convenientlybe supported at the inside of the roll stands. this arrangement of thetensioning apparatus the total tension in the strip equals the pressurein the strut multiplied by a constant, or in other words T equals KP, inwhich K is a constant. This can best be shown by assuming a. practicalspacing of 20 feet between adjacent 4-,high stands .of a tandem orcontinuous mill, and by assuming that the pivot .axes l2 andl3' of theouter ends of the struts are spaced 2 feet from vertical planes passingthrough the axes of the rolls. When so spaced from the rolls of the millstands, the pivot axes l2 and I3 of the struts can readily be supportedat the insides of the roll stands free from interference with the mills,and can be so positioned belowthe inclined planes of the looped orupwardly deflected strip I that the axes of the struts are, within thepractical range of vertical movement of pressure roller 2',substantially parallel with the inclined planes of the strip at eachside of roller 2'. The assumed spacing of 20.feet between the rollstands and 2 feet betweenthe rolls of each stand and As will be shown,in

the pivot axes of the struts are conveniently given in inches in Fig. 3.

Using the nomenclature explained with reference to Fig. 2, the followingequations are apparent:

2T sin a =R 2P sin a=R sin a sin a If sin-a. divided by sin a is heldconstant for all values of the height h of the axis of roller 2 abovethe horizontal line 25, as it substantially is for all values of theangles a and a within the practical range of the height h, then T isequal to KP, in which K is a constant. From the geometry of themechanism the following equations are apparent, in which the amountsexpressed in numerals are those shown on Fig. 3 under the assumptionthat the roll stands are spaced 20 feetapart, and on the furtherassumption that the horizontal distances, 96 inches, be-v tween thepivot axes l2 and I3 and a vertical. line passing through the axesofroller 2' remain.

constant, which they substantially do within the practical range ofvertical movement of roller 2:

/l20 (squared) +h' (squared) sin 11:

126 (squared)+h (squared) V 96 (squared)+h (squared) 14400-l-h.(squared) \l9216+h (squared) Solving the last equation'on theassumption.

that the height h is zero, T equals 1.25P, and

solving it on-theassumption that the. maximum.

height h is 30 inches, T equals 123?. Amaximum height of 30 inches isthe practical maximum height of a loop between rollstands that arespaced 20 feet apart, it being understood that.

a tensiometermechanism of .the..type herein disclosed is equipped withmechanism, well known in the art, for so controllingthe relative peripheral speeds of the working rolls that the length of strip between tworoll stands will permit looping of the strip within minimum and maximum.

limits. The solving of thelast of the. above equations shows that thetension T in a strip is constant throughout a height h of. from-0 to 30,Therefore, to obtain a constant known total tension in-.a.v strip in thearrangement shown in Fig. 3 .the'

inches to within plus orminus 0.8%.

required pressure P applied to the extensible strut may be obtained bydividing the known tension by l.24, which is the average of 1.25.and.

From the foregoing it is plainthat, for all practical spacings ofrollstands, a constant force 7 applied to the extensible strut acting in alinepassing through itspivot points will result in maintaining aconstant tension in the strip ineither hot or coldrolling mills.Ifthe-spacingof roll stands is materially less than 20feet, asit.usually is in cold rol1ing;.mi1ls, themaximum. permissible height of theloop is correspondinglydiminished below 30 inches, and if the spacing ofthe roll stands is increased beyond 20 feet the maximum permissibleheight of the loop may be increased beyond 30 inches. Similarly, thespacing of the lower pivot points of the struts from the sides of therolls may be varied within practical limits without varying theprinciple of operation of the tensioning mechanism or the resultobtained by it.

According to the provisions of the patent statutes, we have explainedthe principle of our invention and have diagrammatically illustrated,and have described, practical embodiments of it. However, we desire tohave it understood that, within the scope of the appended claims, theinvention may be practiced with apparatus different than thatdiagrammatically illustrated.

We claim:

1. A tensioning device for subjecting a strip to constant tensionbetween two zones comprising a vertically movable idle roller below thestrip extending transversely thereof between the two zones andconstructed to bear upon the lower face of the strip and deflect itupwardly at substantially equal inclinations to the horizontal at eachside of the roller, a pair of struts, at least one of which isextensible, each pivotally connected at one of its ends to and forsupporting said roller and directed laterally and downwardly therefrom,one towards one and the other towards the other zone, the lower outerends of.

said struts being pivotally supported in fixed positions proximate tothe points of upward deflection of the strip to permit said struts tomaintain substantially parallel relationship with respect to saidupwardly deflected strip, and means for applying a substantiallyconstant force to said extensible strut acting between and in a linepassing through the end pivots thereof to vary the distancetherebetween, thereby varying the elevation of said roller.

2. A tensioning device for subjecting a strip to constant tensionbetween two zones comprising a vertically movable idle roller below thestrip extending transversely thereof between the two zone andconstructed to bear upon the lower face of the strip and deflect itupwardly at substantially equal inclinations to the horizontal at eachside of the roller, a pair of struts, each pivotally connected at one ofits ends to and for supporting said roller and directed laterally anddownwardly therefrom, one towards one and the other towards the otherzone, the lower outer ends of said struts being pivotally supported infixed positions proximate to the points of upward deflection of thestrip to permit said struts to maintain substantially parallelrelationship with respect to said upwardly deflected strip, one of saidstruts bein extensible comprising a cylinder having a piston therein anda rigid member connected to said piston, the other of said struts havingthe same length between its pivot points in all vertical positions ofsaid roller, and means for applying a constant pressure to said cylinderto extend said extensible strut in a direction passing through thepivots thereof to vary the distance therebetween, thereby varying theelevation of said roller.

3. A tensioning device for subjecting a strip to constant tensionbetween two zones comprising a vertically movable idle roller below thestrip extending transversely thereof between the two zones andconstructed to bear upon the lower face of the strip and deflect itupwardly at substantially equal inclinations to the horizontal at eachside of the roller, a pair of struts, each pivotally connected at oneend to and for supporting said roller and directed laterally anddownwardly therefrom, one towards one and the other towards the otherzone, the lower outer ends of said struts being pivotally supported infixed positions proximate to the points of upward deflection of thestrip to permit said struts to maintain substantially parallelrelationship with respect to said upwardly deflected strip, one of saidstruts being extensible, means for applying a constant force to saidextensible strut acting between and in a line passing through the endpivots thereof to vary the distance therebetween, thereby varying theelevation of said roller, and means for balancing the weight of saidroller and struts.

MORRIS D. STONE. JOSEPH I. GREENBERGER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,886,232 Sykes July 5, 19322,296,753 Wilton Sept. 22, 1942

